A rotorcraft may include one or more rotor systems. Examples of rotor systems include main rotor systems and tail rotor systems. A main rotor system may generate aerodynamic lift to support the weight of the rotorcraft in flight, and thrust to counteract aerodynamic drag and to move the rotorcraft in forward flight. A tail rotor system may generate thrust in correspondence to rotation of the main rotor system in order to counter torque created by the main rotor system.
US 2008/075591 A1 discloses a method for automatically reducing the effect of a component of an external force that is laterally incident on a rotorcraft. A signal of the rotorcraft indicative of and proportional to the component is monitored. An absolute value of the signal and a preset high limit are compared. If the absolute value is greater than the preset high limit, manual heading control of the rotorcraft is disabled and the heading of the rotorcraft is adjusted with respect to the external force so as to decrease the lateral component of the external force experienced by the rotorcraft.
US 2014/361118 A1 discloses a method of limiting vertical axis augmentation in a rotorcraft, the method comprising: measuring a torque with a sensor; deriving a comparison of the torque to a lower torque limit, using a computer processor; and adjusting a vertical axis control command based upon the comparison of the torque to the lower torque limit.
U.S. Pat. No. 6,259,975 B1 discloses a flight control system for an aircraft, particularly for a helicopter receives a number of items of information, especially the position of flight control members of said aircraft, and sends, depending on these items of information, control inputs to controls of the aircraft. The flight control system includes at least one sensor which measures values representative of the flight of the aircraft and computing means which generate, at least from these measured values and from the positions of flight control members, corrected control inputs which are sent to the controls and which enable control of the lateral speed of the aircraft with respect to the ground, without varying the course of the aircraft.
US 2016/291598 A1 discloses a flight vehicle control and stabilization process that detects and measures an orientation of a non-fixed portion relative to a fixed frame or portion of a flight vehicle, following a perturbation in the non-fixed portion from one or both of tilt and rotation thereof. A pilot or rider tilts or rotates the non-fixed portion, or both, to intentionally adjust the orientation and effect a change in the flight vehicle's direction. The flight vehicle control and stabilization process calculates a directional adjustment of the rest of the flight vehicle from this perturbation and induces the fixed portion to re-orient itself with the non-fixed portion to effect control and stability of the flight vehicle. The flight vehicle control and stabilization process also detects changes in speed and altitude, and includes stabilization components to adjust flight vehicle operation from unintentional payload movement on the non-fixed portion.
US 2008/308682 A1 discloses a flight control system for an aircraft that receives a selected value of a first parameter, which is either the airspeed or inertial velocity of the aircraft. A primary feedback loop generates a primary error signal that is proportional to the difference between the selected value and a measured value of the first parameter. A secondary feedback loop generates a secondary error signal that is proportional to the difference between the selected value of the first parameter and a measured value of a second flight parameter, which is the other of the airspeed and inertial velocity. The primary and secondary error signals are summed to produce a velocity error signal, and the velocity error signal and an integrated value of the primary error signal are summed to produce an actuator command signal. The actuator command signal is then used for operating aircraft devices to control the first parameter to minimize the primary error signal.
US 2007/221780 A1 discloses a method and apparatus for automatically controlling the flight of a tiltrotor aircraft while the aircraft is in flight that is at least partially rotor-borne. The method and apparatus provide for automatically tilting nacelles in response to a longitudinal-velocity control signal so as to produce a longitudinal thrust-vector component for controlling longitudinal velocity of the aircraft. Simultaneously, cyclic swashplate controls are automatically actuated so as to maintain the fuselage in a desired pitch attitude. The method and apparatus also provide for automatically actuating the cyclic swashplate controls for each rotor in response to a lateral velocity control signal so as to produce a lateral thrust-vector component for controlling lateral velocity of the aircraft. Simultaneously, collective swashplate controls for each rotor are automatically actuated so as to maintain the fuselage in a desired roll attitude. The method and apparatus provide for yaw control through differential longitudinal thrust produced by tilting the nacelles.
JP 2007 290646 discloses a solution to keep an unmanned helicopter at a stable attitude even when it has a suddenly rising cross-wind. This is done by bringing the nose of the unmanned helicopter nearby into line with a windward direction as shown by a sign a when it has the suddenly rising crosswind, for instance, at the time of circling during a high speed flight while receiving a following wind. Thus, the project area of the body receiving the wind is decreased, and the wind is dissipated. Therefore, the roll angle of the body can be reduced, and consequently, the attitude of the unmanned helicopter 1 can be stabilized.
EP 0 455 580 A2 discloses a ground-plane-referenced, acceleration signal and Doppler velocity signal utilized by a complementary filter to provide a complementary velocity signal which is transformed to an inertial coordinate referenced velocity signal utilized in combination with a GPS position signal by a complementary filter to provide a complementary, position error signal that is transformed to a ground-plane-referenced, position error signal and summed with a wind speed signal calculated from the difference between air speed and the aforementioned complementary velocity signal to provide a pitch command signal. A similar system is utilized to provide a roll command signal. The system is gated by signals which are determinative of the aircraft meeting predetermined flight conditions.